The Guardian columnist Owen Jones has said he believes he was targeted in an unprovoked late-night attack over the weekend because of his anti-fascist politics and warned that divisive rhetoric is emboldening some on the far right to become violent.

The writer and activist was out celebrating his 35th birthday and was leaving a bar near King’s Cross at around 2am on Saturday morning when a group of men “charged out of the pub with military precision” and hit him from behind while he was saying goodbye to friends.

“They kicked me in the back, I was knocked down, then they kicked me in the head and back,” Jones said. Some of his friends were also hurt. “Three of them were punched, my partner was punched in the end. They were only trying to defend me.”

The attackers ran off into the night and police are seeking up to four people. Jones said there was “no question that it was anything other than a targeted attack”.

Anti-fascist campaigners have told Jones there had been “chatter online” about the incident at the Lexington pub on Pentonville Road hours before he went public about it on Saturday afternoon.

“What they had heard was that far-right football hooligans were boasting in closed groups along the lines of ‘Owen Jones has been done in, in Islington,’” Jones said.

News of the attack prompted an outpouring of support and sympathy. The Labour leader, Jeremy Corbyn, said: “An attack on a journalist is an attack on free speech and our fundamental values.”

Katharine Viner, the Guardian’s editor-in-chief, said the newspaper deplored the “outrageous attack”. She added: “Violent assaults on journalists or activists have no place in a democratic society.”

Jones said: “I’m just a symptom of a wider phenomenon, an emboldened, increasingly violent far right.” He said he believed there had been a “dramatic escalation” in the level of threat faced by him and others in the last eight or nine months.

He said far-right protesters were being radicalised by what he described as “hate preachers” in politics and in some parts of the media. “We all know who the hate preachers are: one of them is the most powerful man on earth, the occupant of the White House. But there are also multiple politicians and people in the mainstream media who deliberately stoke tensions, who demonise minorities and who demonise the left,” he said.

Jones said there had been no previous interaction with the attackers. “I think they were waiting for us to leave the pub and make their move,” he said, adding that he was relieved he had not been alone.

Police arrived at the scene promptly and no medical treatment was required, although Jones was left with “a bump on the back of my head”. He is now helping police to track down his attackers.

In January, after Jones spoke at an anti-austerity demonstration, he was subjected to homophobic abuse by an aggressive group of pro-Brexit protesters in Trafalgar Square. One video showed them chanting “Jonesy is a homo” in an attempt to intimidate him. A second video showed him being mobbed by aggressive protesters, forcing the police to intervene.

He said he would not make any changes to his schedule of media and political activities, although he had taken security advice in the past.

“The far right are trying to achieve political ends through coercion and violence, so there’s no way I’m going to change. Yes, I’ll take precautions, but I’ll be at my protests, fighting against racism, for socialism. What could I have done? Not had a birthday thing? Of course everybody should be vigilant, but I’m not going to be intimidated. I’m not changing my politics.”

The Metropolitan police said officers in Islington were investigating “after a man in his 30s reported being assaulted outside a pub in Pentonville Road, N1 at approximately 0200hrs on Saturday 17 August. He was attacked by up to four males who also assaulted his friends when they attempted to intervene. No arrests have been made. Local CCTV footage will be reviewed.”